1. Field of the Invention
The present invention relates to an in-car telephone system wherein a portable telephone unit and a hands-free unit are communicatively connected, whereby conversations through the portable telephone unit can be held using a speaker and a microphone of the hands-free unit, the hands-free unit and the portable telephone unit.
2. Description of the Relevant Art
When one speaks over the telephone while riding in an automobile (especially operating an automobile), one cannot hold a handset in one's hand, or to hold a handset in one's hand often makes driving dangerous. Therefore, hands-free units whereby conversations can be held using a microphone and a speaker arranged in the interior of a car have been used so far. Conventionally, mobile telephone units designed specifically for cars had been used as telephones mounted on cars, but nowadays, telephone units of a dual-purpose type with which hands-free conversations can be held by connecting a portable telephone to a hands-free unit arranged in a vehicle through a connector are becoming more common because of widespread use of portable telephones.
However, in cases where a portable telephone is used as a part of a hands-free unit, or in cases where a portable telephone which had been used as a part of a hands-free unit is used as a normal portable telephone, it becomes necessary to disconnect communication between the portable telephone and the hands-free unit by detaching the portable telephone from the connector or the like. For the disconnecting operation, it is necessary to end the telephone conversation, or when the disconnecting operation is conducted during talking over the telephone, the telephone conversation is broken off. Therefore, in the case of getting in or out of a car during a telephonic communication, one needs to make a call again at great inconvenience.